Leaving aside laser power, frequency and footprint. The main thing that will effect process efficiency will be the absorption efficiency of work piece. Pre-treatment of the work piece by fine grit blasting and graphite coatings should increase absorptivity, thus increasing overall process efficiency.

Another thought, assuming we are talking about martensitic transformation of steel, is to be careful with selecting the optimum condition/microstructure for your steel. I would assume this is similar to induction hardening where coarse microstructures require higher temperatures or longer time at temperature to austenitise properly than fine microstructures.
Hardened and tempered/spherodised conditioned steels are usual best and again should increase process efficiency over using say annealed or normalised steels.